linux-kernel - Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP

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Date:   Fri, 9 Dec 2016 22:03:16 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     kernel-hardening@...ts.openwall.com
Cc:     Andy Lutomirski <luto@...capital.net>,
        linux-crypto@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [kernel-hardening] Re: Remaining crypto API regressions with
 CONFIG_VMAP_STACK

On Sat, Dec 10, 2016 at 01:32:08PM +0800, Herbert Xu wrote:
> On Fri, Dec 09, 2016 at 09:25:38PM -0800, Andy Lutomirski wrote:
> >
> > > The following crypto drivers initialize a scatterlist to point into an
> > > ablkcipher_request, which may have been allocated on the stack with
> > > SKCIPHER_REQUEST_ON_STACK():
> > >
> > >         drivers/crypto/ccp/ccp-crypto-aes-xts.c:162
> > >         drivers/crypto/ccp/ccp-crypto-aes.c:94
> > 
> > These are real, and I wish I'd known about them sooner.
> 
> Are you sure? Any instance of *_ON_STACK must only be used with
> sync algorithms and most drivers under drivers/crypto declare
> themselves as async.
> 

Why exactly is that?  Obviously, it wouldn't work if you returned from the stack
frame before the request completed, but does anything stop someone from using an
*_ON_STACK() request and then waiting for the request to complete before
returning from the stack frame?

Eric